A shoe calender is formed of one or more calendering nips, where calendering is performed. Each calendering nip, in turn, comprises a heated thermo roll and an endless belt, which is located opposite this and under which a shoe element pressurized by loading means is provided at the roll nip. The loading means comprises two rows of hydraulic cylinders, one of the rows of hydraulic cylinders being located at the trailing edge of the shoe element and the other one at the leading edge of the shoe element. The endless belt rotates about the stationary plate frame of the shoe roll located opposite the thermo roll. The fiber web runs between one or more roll nips in the shoe calender, its surface being thus calendered with the desired smoothness, thickness, opacity and glaze (quality variables of the fiber web). The quality variable values, in turn, depend on the actions to which the fiber web is subjected in the calendering nip, i.e. the nip process. The nip process is affected by the roll nip condition, i.e. the total weight, the weight distribution and the temperature of the roll nip, and also the humidity and temperature of the fiber web when running through the nip, and finally the calendering period, i.e. the residence time of the fiber web in the roll nip.
The factors acting on the nip process are usually controlled by the following control variables:                the linear pressure acting on the roll nip condition is formed by the mutual pressure of the shoe roll and the thermo roll against each other, this pressure being adjustable for instance by varying the weight of the shoe roll and the thermo roll. The linear pressure in the shoe calender also depends on the overall loading pressure of each shoe element.        the humidity and temperature of the fiber web can be controlled by the dewatering degree of the fiber web and by blowing steam onto the fiber web surface before the roll nip.        the roll nip temperature is primarily controlled by the thermo roll temperature, which has been generated either by internal or external heating of the roll, by means of a separately controlled actuator, induction heater, heat blower or the like.        the calendering period depends on the fiber web rate and the roll nip length, the former being used as an active variable for controlling the nip process.        
Besides the active control variables mentioned above, the state of the calendering nip in shoe calendering depends on the overall loading pressure of the shoe element and on the weight distribution between the leading edge and the trailing edge of the shoe element. In this context, the leading edge of the shoe element stands for the edge that is parallel with the longitudinal axis of the shoe roll and that the fiber web contacts as it reaches the roll nip, whereas the trailing edge stands for the edge of the shoe element that is parallel to the longitudinal axis of the shoe roll and that the fiber web leaves as it is detached from the roll nip.
The inclination of the shoe element is varied by means of the loading pressure difference between the rows of hydraulic cylinders provided under the leading and trailing edge of the shoe element, so that the load exerted by the hydraulic cylinders on the trailing edge of the shoe element is greater than the load exerted on the leading edge. The loading pressure difference between the trailing edge and the leading edge of the shoe elements is called “tilt”, in other words, the load exerted on the trailing edge of the shoe element exceeds the load on the leading edge by the tilt. In shoe calenders, the tilt and the total pressure of the shoe element act on the state of the roll nip and thus affect the calendering result.